Downsize PVC to fit blast gates

When I installed a central ductwork system for my dust collector, I used 4" PVC pipe instead of steel and saved 75 percent on the cost. But the inside diameter of the 4" PVC is 1/8" too large for blast gates designed for steel ducts. My dad and I solved that problem by shrinking the PVC pipe slightly with a propane torch.

To soften the PVC for the joints, we slipped a hose clamp over the pipe and carefully heated the pipe until it softened. With the pipe end soft, he slipped the fitting into the pipe, slid the hose clamp up near the end, and tightened it to snug-up the softened PVC end. Once the pipe cooled and hardened, we removed the hose clamp to use for the next joint.

Finally, I secured the blast gate to the pipe with a sheet metal screw. With no tape, glue, or steel, and only a single hose clamp, it's a clean, simple way to build an inexpensive but effective collection system.